Method of making microminiature incandescent lamps



METHOD OF MAKING MIGROMINIATURE INCANDESCENT LAMPS Original Filed March 4, 1960 2 Sheets-Sheet 1 u "5B A l J U i 30 i 'La FIG. 5

/A/VE/W'OE, www JHK/v/IP ATTORNEYS July 13, 1965 D. J. BELKNAP 3,193,906

METHOD 0F MAKING MIGROMINIATURE INGANDESCENT LAMPS Original Filed March 4. 1960 2 Sheets-Sheet 2 ATTORNEYS United States Patent C) 3,193,906 METHOD F MAKING MHCRGMINIATURE INCANDESCENT LAMPS Donald J. Belknap, 302 Patterson Court, Takoma Park, Md.

riginal application Mar. 4, 1960, Ser. No. 12,877, now Patent No. 3,040,204. Divided and this application Mar. 6, 1962, Ser. No. 193,030

Claims. (Cl. 29-2511) (Granted under Title 35, US. Code (1952), sec. 266) This application is a division of application Serial No. 12,877, led March 4, 1960, now Patent No. 3,040,204 issued June 19, 1962.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to incandescent lamps in general, and more specifically to a method of making microminiature lamps.

New electronic systems are continually being developed today. Many of them, such as giant computers, are extremely complex. To keep the size and power requirements down, it becomes very desirable to miniaturize as far as possible the electronic components and circuitry. Long-range missiles and space probes in particular require small, compact, electronic circuits. The development of the transistor and the use of printed circuit techniques have contributed greatly to efforts in the eld of electronic miniaturization.

Extremely compact circuits have been constructed using hearing-aid type components and printed circuitry, resulting in component densities of about 150 components per cubic inch. Recently two-dimensional circuitry has been developed in which the active elements of electronic components, including transistors, are mounted on small ceramic wafers and are electrically connected by employing photolithographic techniques. By placing up to fifteen components on a one-half inch square ceramic wafer, the component density has been increased to about two thousand components per cubic inch.

With these advances in microelectronics, an urgent need developed for small, low-current indicator lamps to be used for read-out purposes in binary counting circuits. Available lamps were completely incompatible in size with other circuit components being used and in general required currents larger than the transistors could provide.

Broadly therefore it is an object of this invention to provide a microminiature incandescent lamp.

Another object of this invention is to provide a method for constructing a microminiature incandescent lamp.

Still another objective is to provide means whereby the said microminiature lamp can be simultaneously fabricated and tested.

The specific nature of the invention, as well as other objects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawing, in which:

FIG. 1 illustrates a microminiature lamp constructed in accordance with the instant invention.

FIGS. 2 to 4 schematically illustrate the basic steps for fabricating the lamp shown in FIG. l.

FIGS. 5, 5A and 5B show the jig by which the lamp components can be properly oriented.

FIGS. 6, 6A and 6B illustrate the means required for sealing the microminiature lamp shown in FIG. 1.

According to this invention, microminiature incandescent lamps can be constructed which measure less than 0.10 inch in length and 0.025 inch in diameter. Light from these lamps operating at l to 11/2 volts and 25 to 30 milliamperes of current is easily visible from any point in a normally lighted room. They thus meet the need forv indicator lamps which will operate on the limited currents available in todaysmicroelectronic computer circuitry. As a consequence or" their small physical size and weight, these lamps are very rugged and able to withstand considerable shock and vibration.

FIG. 1 illustrates a microminiature lamp 10 constructed in accordance with this invention. Lamp 10 comprises a pair of leads 11 and 12, a glass envelope 13 and a llament coil 14 encapsulated in the envelope and attached to the ends of leads 11 and 12. Leads 11 and 12, which extend from opposite ends of the microminiature lamp 10, are 0.75 inch lengths of .005 or 0.003 inch diameter platinum wire.

Referring now to FIG. 2, ends 15 and 16 of leads 11 and 12 are flattened by any conventional method, such as stamping or hammering. Cylindrical glass sleeves 19 and 20 are thereafter added to leads 11 and 12. Sleeves 19 and 20 are substantially identical in size and shape and may have a diameter of 0.030 inch for a somewhat smaller lamp. These sleeves are provided with bores 19a and 20a, which are slightly larger in diameter than the 0.005 or 0.003 inch diameter of leads 11 and 12 but are preferably not large enough to pass over flattened ends 15 and 16. The glass sleeves, when so positioned on leads 11 and 12, are heated in a small ame until they become somewhat spherical and become fused to the platinum leads. The spheres so produced are referred to by numerals 19' and 20. Flattened ends 15 and 16 are then cut to a length approximately 0.015 inch and thereafter bent back to form hooks or eyelets 21 and 22 (FIG. 3) which can receive the opposite ends of coil 14.

The beaded leads can also be prepared by spacing a number of the cylindrical glass sleeves 19 and 20 about one inch apart along a length of .005 or .003 inch platinum wire, which is supported by two posts with a means provided for applying slight tension to the wire. Current is passed through the wire to heat it to a temperature Where the sleeves are sealed to it. The beaded leads are then separated by cutting, the ends near the beads being attened and formed into hooks or eyelets.

For a 1.5 volt lamp, coil 14 (FIG. 1) is formed of approximately to 30 turns of 0.00025 inch diameter tungsten wire on a 0.001 inch diameter mandrel. Glass envelope 13 (FIG. l) is composed of a cylindrical glass tube 23 (FIG. 4) into which the glass beads 19' and 20 will tit with preferably not more than 1 or 2 mils clearance. The thickness of tube 23 is approximately 2 mils. A tube length in the range of 0.05 to 0.09 inch is sulicient for a 25 turn filament. Tube 23 can be slid over beads 19' and 20 until end 24, which has been turned in very slightly by heating, contacts glass bead 19. The turnedin end 24 permits the tube 23 to be sealed while hanging substantially vertically from bead 19.

In order to seal the glass envelope 13 with the filament coil 14 inside, a jig 26 (FIG. 5) is provided. Iig 26 comprises an insulating base 27 which supports a pair of substantially identical lamp lead supports 23 and two pairs of substantially identical heating cylinder lead supports 30. A typical cylinder lead support 30 is shown in FIG. 5a as consisting of upper and lower support plates 34 and 35, respectively. The lower support plate is attached permanently to the base 27 by machine screws (not shown) passing up through the base. Machine screws 36 are used to fasten the upper plate 34 to the lower plate 35. A V-shaped groove 37 is formed in the lower plate 35 and it is in this groove that one cylinder lead 33 can be placed and fixed by tightening the machine screws 36 against upper cylinder lead support plate 34. Cylinder leads 38, 38', 38, and 38' are connected to opposite sides of hollow molybdenum heating cylinders 40 and 41. Heating cylinders 40 and 41 (FIG. 5) are molybfin FIG. 6. VThe bell u Y denum tubes with wall Ythicknesses of approximateily 0.002 inch and internal diameters ofY approximately 0.060 inch. Thus, in assembling or removing a lamp the glass envelope13 `can berslidthrough heating cylinders 40 and which' a' pair of `cylinder leads 38 canrpass without touching the supports, V-shaped groove 46, plate 42' and machine screws 47 'cooperate toreceive and hold the lamp` leads 11 and 12 inthe grooves'46.

Leads'll and 12 are initially inserted throughheating..V cylindersh and 41 andthe ends placedin grooves; 45 in the lower lead, support plates 43, the upper lead-supportv4 plates 42' being removed'.` YGlass tube 23 is initially slid back over-lead 11 to uncover bead 1'9V and expose hook 2l..` t

in Y'current and voltage occurs, current to the cylinders is yimmediately turned Voff.' Air is thenadniitted to the bell jar, the jig taken out, and the Vcompleted lamp is removed from the jig. Y

A microminiature lamp having a filament of 25 turns of 0.00025 inch tungsten wire wound on a 0.001 inch mandrel` and constructed in accordance with the method of n this invention typically has the following characteristics:

- By varying the wirefsize and the' turns of the' rament those skilled inthe art can construct lamps by theme'thod of this invention having other voltage and current char- The heating cylinder leads 38, 38",v 36, 'andr38f" arev v fixedv between the upper and lower support `plates of supports 30 in a position Where the ends ofthe heating;y

cylinders almost contact, supports 28, thereby making:

il'amentf The endsof coil 14I are placed in hooks Vor eyelets ,21; and'ZZ, and'these hooks or eyelets arethere-v` after closed tightly onto theVV ends of the coil by pinching.v Alternately, the filament can be attached to one or bethy leads-before they are placed inthe jig. The upper lead support Yplates 42gareV then placed upon'lowe'r lead sup- Y accessible the central region of the jigfor'att-aching the Y acteristic's. Y y Y The lamps produced by the method-of lthis invention are well adapted because of their small power requirementfor use in" all transistorized circuits such' as computers, binary 'y counters, switchboards and control panels.

rquence ofY their very smallfilame'nts which are positioned In conse# by"closely spaced supports, Ytheyrcan be used' in optical' Y systems Yrequiringaprecisely positioned', point-source of' light. Their small envelopeY size makes them usefull asf anillurnination sourcev for very smallpr'obes and medical' endosco'pes.V BecauseY of their lightness in weight, they cank be mounted' on the pointeur-tipsv of aircraft panel Y meters Yor other moving objects toVv indicate" position or` portplates'h and screws 47 tightened slightly against plate 42. The endsof leads 11' and 121 are then pulledl slightly apart to give small'separation betweenthe turns of coil 114., Machine; screws 47 are securely tightenedso` alignedfwiththeends of the lampi-150, whereupon screws 36 are again-tightened. i Y i .lig 26 is thenplaced vertically in a lthree inch tall bell*l jar 48 (FIG. 6) and connection made to leads'4t9,vv 50,'- 51, 52, 53 andf54 sealed through the bell jar base e5.

These leads *supportV jig 261in the vertical? positionjas shown" jar is pumped out to a vacuum of about l l0F4 mm. Hg. Y The two cylinders 40 and 41 are connectedelectrlcally in seriesV as shown schematically in-fFIG. 6a and a slide-` wire'frheostat 56 having slide 57 isplaced acrossV the com-l bination. Whencurrent is applied,l cylinders 40 and 41A,

trajectory.VV They'can also' be used'` in arrays t'o` print outl numbers, graphs, or picturesv with a :frequencyV response' not attainable by prior art incandescent lamps.

It willv Abe apparent that the,` embodiments shown are only exemplary and that various modifications can beV made'in construction and'arrangernent within the'scope of l the Vinventionasdefined in the'appended claims. *For eir-l ample, the glass envelope may be' a-hollow cylinderwith one end sealed; VBoth-pairs of leads may be' fusedi'n" parallel relationship through a single glass beadi The' ilamentrcan then be fixed' to the ends ofthe leads across Y' the gap between these ends. `The bead' canther'e'forebe will"radiate'heat to the lamp ends. The circuit showninl Y FIG. 6a makes it possible to bake out the lamprwith they two cylinders-heated tov about thersameztemperatute' and then to turn upV the heatY in turn `oneach lof the twofusedv in the open endl ofrthe .envelopewby'the method' disclosed above while the envelope and thefheating'cylindersare under vacuum. v

lfclaiin as my invention:

j l; A" method of constructing a comprising the steps of fusing aglass bead toeach of a pai'rrof vlead wires, formingthe ends ,of each leadwir'el into a'hook, inserting the' ends 'ofja lament coil into eachrhook so formed, pinchingthe hook together to fixi said filament coil between said leads and eacli'gla'ss bead, and'then fusing the ends of a hollow glass-tubeto each bead, ina vacuum. Y. i

` 2;*Ai'-mcthod of constructing microminiature incan` descent lamps, comprising.' the Vsteps of V'fusing a"gla'ss bead to'eachend of a'pair of opposed wire' leads, formanda variable resistor 163 connectedin serieswith fila-" ment14 and 'arrvoltmetie'rgfl connected -in shunt withfilafV ment" 14. V`By-adjusting the resistor 63, the lamp isoperated, during the sealing of? the secondendrat a voltage.`

' a glass sleeve, heating the glass beadsV and the ends ofsaid" Vglass sleeve -in a vacuum until said glass sleeye and 'beads fuse together.

Y 3; A method'4 of constructing mierorniniature'V incan- Y descent'lamps, comprising fthe steps of `fusing a glass bead to each end Vof .a Apairj of opposedwire leads, forming ment 149' causin'glthe resistance o'fj'the iilarnent 1410 decrease. VFlhis decrease in resistance causes vthe current v indicated byV milliammeteral 'tofincrease and the voltage- Vindicated by voltmeter'el to decrease.VV When this-changej Y hooks at the extremities of-each lead,inserti1'1g` the ends Vonta filament coil into eachVv hook so formed, pinching the hooks to fix said/lam'entrbetweensaid leads and I each glass bead, heatingone end of a hollow glass' tube having an internal diameter slightly larger than theY diameter ofA each'beaduntil said endturns'in sufiiciently to contact ltheY Yperiphery ot Voney glass-bead, suspending said rnicrominiaturev lamp,

glass tube by the turned-in end from one bead, the other end of said `tube encasing the other bead and said lilament coil fixed between said leads and each glass bead, then successively heating each end of said tube, in a vacuum until the beads and tube fuse together.

4. A method of constructing microminiature incandescent lamps, comprising the steps of fusing a glass bead to each end of a pair of opposed wire leads, forming hooks at the extremities of each lead, inserting the ends of a filament coil into each hook so formed, pinching the hook-s together to fix the filament coil between said leads and each glass bead, heating one end of a hollow glass tube having an internal diameter slightly larger than the diameter of each glass bead until said end turns in sufficiently to contact the periphery of one glass bead, suspending said glass tube by the turned-in end from one glass bead, the other end of said glass tube encasing the other glass bead and said filament coil fixed between said leads and each glass bead, then positioning a heating element adjacent each end of the suspended glass tube, heating each end of `said suspended glass tube in a vacuum with the positioned heating elements to bake out the lamp assembly, then increasing the heat in turn applied to each end of said suspended glass tube in a vacuum by said heating elements to successively fuse said glass beads to said glass tube.

5. A method of constructing microminiature incandescent lamps, comprising the steps of fusing a glass bead to each end of a pair of opposed leads, forming hooks at the extremities of each lead, inserting the ends of a lament coil into yeach hook so formed, pinching the hooks together to fix the filament coil between said leads and each glass lead, heating one end of a hollow glass tube having an internal diameter slightly larger than the diameter of each glass bead until said end turns in suf- 3 ficiently to contact the periphery of one glass bead, suspending said glass tube by the turned-in end from one glass bead, the other end of said glass tube encasing the other glass bead and said filament coil fixed between said leads and each glass bead, then positioning a heating element adjacent each end of the suspended glass tube, heating each end of said suspended glass tube in a vacuum with the positioned heating elements to bake out the lamp assembly, then increasing the heat applied to one Iend of said suspended glass tube in a vacuum to fuse one of said glass beads to said glass tube, then passing a current through said filament coil suiiicient to produce slight reddening of the filament while simultaneously increasing the heat applied to the other end of said glass tube in a vacuum to fuse the other of said glass bead to said glass tube, and monitoring the filament coil characteristic during the fusing of said other glass bead to said glass table.

References Cited by the Examiner UNITED STATES PATENTS 461,797 10/91 Marshal 29-25 .14

722,702 3/03 Hanks 29--25.l4 1,755,983 4/30 Erber et al 29-25.13 2,079,893 5/37 Bain et al 29-25.13 2,199,879 5/40 Deroche 29-155.64 2,685,762 8/54 Mullan 29--25.19 2,832,016 4/58 Bakalar 29-25.3 2,940,220 6/60 Roeber 29-25.19 2,992,874 7/61 Germeshausen 316-19 3,069,583 12/62 Swasey 29-25.13

FOREIGN PATENTS 1,167,971 12/58 France.

I RICHARD H. EANES, IR., Primary Examiner.

LEON PEAR, Examiner. 

4. A METHOD OF CONSTRUCTING MICROMINIATURE INCANDESCENT LAMPS, COMPRISING THE STEPS OF FUSING A GLASS BEAD TO EACH END OF A PAIR OF OPPOSED WIRE LEADS, FORMING HOOKS AT THE EXTREMITIES OF EACH LEAD, INSERTING THE ENDS OF A FILAMENT COIL INTO EACH HOOK SO FORMED, PINCHING THE HOOKS TOGETHER TO FIX THE FILAMENT COIL BETWEEN SAID LEADS AND EACH GLASS BEAD, HEATING ONE END OF A HOLLOW GLASS TUBE HAVING AN INTERNAL DIAMETER SLIGHTLY LARGER THAN THE DIAMETER OF EACH GLASS BEAD UNTIL SAID END TURNS IN SUFFICIENTLY TO CONTACT THE PERIPHERY OF ONE GLASS BEAD, SUSPENDING SAID GLASS TUBE BY THE TURNED-IN END FROM ONE GLASS BEAD, THE OTHER END OF SAID GLASS TUBE ENCASING THE OTHER GLASS BEAD AND SAID FILAMENT COIL FIXED BETWEEN SAID LEADS AND EACH GLASS BEAD, THEN POSITIONING A HEATING ELEMENT ADJACENT EACH END OF THE SUSPENDED GLASS TUBE, HEATING EACH END OF SAID SUSPENDED GLASS TUBE IN A VACUUM WITH THE POSITIONED HEATING ELEMENTS TO BAKE OUT THE LAMP ASSEMBLY, THEN INCREASING THE HEAT IN TURN APPLIED TO EACH END OF SAID SUSPENDED GLASS TUBE IN A VACUUM BY SAID HEATING ELEMENTS TO SUCCESSIVELY FUSE SAID GLASS BEADS TO SAID GLASS TUBE. 